Tris-aryl-s-triazines in which at least one of the aryl groups has an hydroxy group ortho to the point of attachment to the s-triazine ring are well-known UV absorber light stabilizers. Such tris-aryl-s-triazines protect organic polymers from the deleterious effects of actinic light.
U.S. Pat. Nos. 3,118,887 and 3,268,474 describe the stabilization of plastic and resinous compositions from UV light by the incorporation of one or more compounds of the class of tris-aryl-s-triazines. The preferred UV absorbers of these inventions are symmetrical tris-(o-hydroxyphenyl)-s-triazines further substituted in the aryl moieties at the 4-position by either an hydroxy or alkoxy moiety. These patents point out that these UV absorbers may be used in coatings based on oil-modified alkyd resins. It is also pointed out that an effective UV absorber should not absorb at all in the visible range so that it exhibits no yellow color visually.
U.S. Pat. Nos. 3,242,175 and 3,244,708 disclose 2,4,6-tris-(2,4-dihydroxyphenyl)-s-triazine and 2,4-bis-(2,4-dihydroxyphenyl)-6-phenyl-s-triazine. The phenyl group of the bis-dihydroxyphenyl compounds may be substituted by halogen, lower alkyl, lower alkoxy or phenyl, preferably in the para position relative to the point of attachment to the s-triazine ring. One or more of the hydroxy groups, preferably those in the para position, of the dihydroxyphenyl rings may be derivatized with alkyl, alkenyl, hydroxyalkyl, hydroxyalkoxyalkyl, halogenoalkyl, cyanoalkyl, carboxyalkyl, carbalkoxyalkyl, phenylalkyl or halogenophenylalkyl groups. These patents also disclose lacquers and films of diverse composition and natural or synthetic resins among other organic materials which may be stabilized from the harmful effects of heat, oxygen and especially actinic light. These patents also disclose that the UV absorbers may be employed in a "filter layer" which would protect the substrate directly beneath said layer or at some distance from it.
U.S. Pat. Nos. 4,619,956 and 4,740,542 disclose the use of synergistic amounts of tris-aryl-s-triazines and hindered amine light stabilizers in polymer film coatings or molded articles against the action of light, moisture and oxygen. Preferably these coatings are acid catalyzed thermoset acrylic or alkyd coatings and most preferably high solids thermoset acrylic coatings. The tris-aryl-s-triazines referred to in these patents are those described in U.S. Pat. Nos. 3,118,887 and 3,268,474. The preferred s-triazine is 4,6-bis-(2,4-dimethylphenyl)-2-(2,4-dihydroxyphenyl)-s-triazine or 4,6-bis-(2,4-dimethylphenyl)-2-(2-hydroxy-4-octyloxy-phenyl)-s-triazine.
U.S. Pat. Nos. 4,826,978 and 4,962,142 disclose a class of tris-aryl-s-triazines useful as ultraviolet screens for polymers, including films and coatings. This subgenus of tris-aryl-s-triazines is substituted at the 2 and 4 positions of the s-triazine ring by a 2,4-dihydroxyphenyl group. The para hydroxy moiety is derivatized with an hydroxyalkyl or an alkylcarboxylate group, specifically either a 2-hydroxyethyl or 2-acetoxyethyl moiety. These specific functional groups allow the UV absorber to become chemically bonded to the polymer being stabilized and therefore are non-extractable. These triazines are further substituted in the 6-position of the s-triazine ting by a phenyl group which is substituted by an electron withdrawing group, preferably halogen, cyano, trifluoromethyl, nitro or acetoxy. These s-triazines are touted as non-yellowing presumedly due to the electron withdrawing substituent on the 6-phenyl moiety.
U.S. Pat. No. 4,355,071 describes stabilized clear coat/color coat systems for automobiles and trucks and teaches that 1-20% by weight of an ultraviolet stabilizer should be incorporated into the color coat. The UV stabilizer will migrate to the upper clear coat and will continue to do so as it is lost from the clear coat due to weathering. Because of this mechanism of action, there will presumedly always be an adequate concentration of UV stabilizer in the clear coat to protect the entire coating system from deterioration. UV stabilizers mentioned in this context include benzophenones, triazoles, triazines, benzoates, etc.
European published application No. 444,323 describes the stabilization of high solids coatings with selected s-triazine UV absorbers, typified by 2,4-di(2,4-dimethylphenyl)-6-[2-hydroxy-4-O(mixed alkyl)phenyl]-s-triazine.
European published application No. 483,488 describes the synergistic combination of a hindered amine and a selected s-triazine UV absorber for the stabilization of polymers including thermoset acrylic coatings. The s-triazine UV absorbers are typified by 2,4-di(2,4-dimethylphenyl)-6-[2-hydroxy-4-(3-ethylhexyl-2-hydroxy- 1-propoxy]phenyl-s-triazine. These compounds and compositions are related to the compounds and compositions of copending application Ser. No. 08/143,525.
Copending application Ser. No. 07/939,507 describes compounds which are useful in photographic applications and which are similar to the instant compounds of formula A.
A coating system commonly used for automobile and truck finishes consists of an electro coat primer, a pigmented base or color coat and a top clear coat. A particular problem occurring with this system is delamination, i.e. a peeling away of the coating from the substrate. It has been found that the cause of delamination is deterioration of the electro coat due to the effects of ultraviolet light that passes through both the base coat and the clear coat. It has now been found that a subgenus of tris-aryl-s-triazines, those based on 2,4,6-tris-(2,4-dihydroxyphenyl)-s-triazine and 2,4-bis-(2,4-dihydroxyphenyl)-s-triazine, is particularly effective in protecting the electro coat of this system when incorporated into either the base coat or the clear coat or both. This significantly inhibits the undesired delamination. Although the prior art points out that a wide variety of tris-aryl-s-triazines are generally useful as ultraviolet screening agents for coatings, the particular utility of this selected subgenus of compounds for the purpose of preventing such catastrophic delamination events is neither disclosed nor suggested.
The instant subgenus of tris-aryl-s-triazines have significant absorbance in the range of 360-400 nm, and in some cases beyond 400 nm. Because these compounds absorb towards the visible spectrum, they are yellow in color. It is believed that the increased absorbance in this region as compared to tris-aryl-s-triazines in general is responsible for the excellent delamination protection afforded by the instant compounds in these coating systems.
Additionally, the instant invention does not require the presence of a hindered amine light stabilizer, but does require that s-triazine derivative of component (d) contain at least two groups on the triazinyl moiety be derived from resorcinol. This distinguishes the instant invention from the closest prior art where only one group on the triazinyl moiety derived from resorcinol is uniformly present in the closest prior art compounds and compositions.
The majority of the compounds disclosed are functionalized with alkyl groups containing at least two oxygen atoms and are more soluble in common coatings solvents than tris-aryl-s-triazines that are functionalized with simple alkyl groups. Common coatings solvents include xylene, methyl amyl ketone, butyl cellosolve, butyl carbitol and methyl isobutyl ketone. This functionality in combination with the high molecular weight of the compounds provides the instant compounds with a low migratory propensity when incorporated into the base coat of a clear coat/base coat system. Because the instant compounds are inherently yellow, minimum migration of the instant compounds into the clear coat is desirable.